feat: complete Epic 0 — foundation migration & infrastructure setup

Stories 0.2-0.5: rename folders→declarations (backend+frontend), configure
Redis for cache/queue/sessions, add foundation database migrations
(permissions, archived_at), replace DeclarationStatus enum with architecture
lifecycle values, create DeclarationObserver for status transition validation
and auto-archive, fix controller status transitions to respect observer rules.

93 tests pass (240 assertions).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Observers/DeclarationObserver.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace App\Observers;
+
+use App\Enums\DeclarationStatus;
+use App\Models\Declaration;
+use Illuminate\Validation\ValidationException;
+
+class DeclarationObserver
+{
+    /**
+     * Handle the Declaration "updating" event.
+     *
+     * Validates status transitions and auto-archives when status becomes "ferme".
+     */
+    public function updating(Declaration $declaration): void
+    {
+        if (! $declaration->isDirty('status')) {
+            return;
+        }
+
+        $oldStatus = $declaration->getOriginal('status');
+        $newStatus = $declaration->status;
+
+        // Handle both string and enum values
+        $oldValue = $oldStatus instanceof DeclarationStatus ? $oldStatus->value : (string) $oldStatus;
+        $newValue = $newStatus instanceof DeclarationStatus ? $newStatus->value : (string) $newStatus;
+
+        $allowed = DeclarationStatus::allowedTransitions()[$oldValue] ?? [];
+
+        if (! in_array($newValue, $allowed)) {
+            throw ValidationException::withMessages([
+                'status' => "Invalid status transition from '{$oldValue}' to '{$newValue}'.",
+            ]);
+        }
+
+        // Auto-archive when status becomes "ferme"
+        if ($newValue === DeclarationStatus::Ferme) {
+            $declaration->archived_at = now();
+        }
+    }
+}